1. Field of the Invention
The present invention-relates to a wireless transmitter device, and more particularly to a wireless transmitter device applicable for example to a wireless communication system in which the accumulated time of data transmission per predetermined duration is limited. The present invention also related to a method of wireless transmission for use in such a wireless communication system.
2. Description of the Background Art
Some types of wireless communication devices limit a period of time for their data transmission. For example, with specified low-power radio stations for use in international transportation data transmission, the total transmission period of time is so regulated that the accumulated transmission period of time per hour, i.e. “total transmission time”, must fall within the range of 360 seconds according to the rules for international transportation data transmission specified low-power radio station defined by the Telecom Engineering Center, “Technical Standards for Specific Facilities”, retrieved on Dec. 28, 2007, on the website, http://www.telec.or.jp/tech/05_equipment/t243—01.html.
Methods that satisfy the above rule include those which follow. The first method is to specify a transmission pause time so that the transmission time per hour is to be 360 seconds or less. For example, after a one-second transmission is completed, transmission must be paused for nine seconds or more so that the transmission time per hour can be shorter than 360 seconds.
In the second method, the total transmission time per predetermined period of time is measured, and the ratio of total transmission time, or “transmission time ratio”, is controlled so as not to be larger than the value of (360 seconds)/(1 hour=3600 seconds)=0.1. When the transmission time ratio almost exceeds the value of 0.1, further transmission is inhibited until the predetermined period of time elapses in order to avoid the transmission time ratio in excess of 0.1. For example, in the case that the predetermined period of time is 60 seconds, the total transmission time is close to exceeding six seconds during the period of 60 seconds, the transmission is inhibited until the period of 60 seconds elapses.
The above-described first and second methods however have the following problems. The first method fails to send data continuously. For example, if a packet is lost, then retransmission of the packet can only start when the pause time elapses after the loss of the packet is detected, which causes a delay before the retransmission.
In the second method described above, the timer must always operate even when no data traffic exists. This increases the power consumption. Especially, when the method is applied to a sensor network in which the communication device is driven by a battery, the timer always causes a problem of power consumption.